sql server single row multiple columns into one column

DDL:

DECLARE @temp TABLE
(
      Reg_No INT
    , Student_Name VARCHAR(20)
    , Subject1 INT
    , Subject2 INT
    , Subject3 INT
    , Subject4 INT
    , Total INT
)

INSERT INTO @temp (Reg_No, Student_Name, Subject1, Subject2, Subject3, Subject4, Total)
VALUES 
    (101, 'Kevin', 85, 94, 78, 90, 347),
    (102, 'Andy ', 75, 88, 91, 78, 332)

Query #1 - ROW_NUMBER:

SELECT  Reg_No = CASE WHEN rn = 1 THEN t.Reg_No END
    ,   Student_Name = CASE WHEN rn = 1 THEN t.Student_Name END
    ,   t.[Subject]
    ,   Total = CASE WHEN rn = 1 THEN t.Total END
FROM (
    SELECT 
          Reg_No
        , Student_Name
        , [Subject]
        , Total 
        , rn = ROW_NUMBER() OVER (PARTITION BY Reg_No ORDER BY 1/0)
    FROM @temp
    UNPIVOT 
    (
        [Subject] FOR tt IN (Subject1, Subject2, Subject3, Subject4)
    ) unpvt
) t

Query #2 - OUTER APPLY:

SELECT t.*
FROM @temp
OUTER APPLY 
(
    VALUES 
        (Reg_No, Student_Name, Subject1, Total),
        (NULL, NULL, Subject2, NULL),
        (NULL, NULL, Subject3, NULL),
        (NULL, NULL, Subject4, NULL)
) t(Reg_No, Student_Name, [Subject], Total)

Query Plan:

Query Cost:

Output:

Reg_No      Student_Name         Subject     Total
----------- -------------------- ----------- -----------
101         Kevin                85          347
NULL        NULL                 94          NULL
NULL        NULL                 78          NULL
NULL        NULL                 90          NULL
102         Andy                 75          332
NULL        NULL                 88          NULL
NULL        NULL                 91          NULL
NULL        NULL                 78          NULL

PS: In your case query with OUTER APPLY is faster than ROW_NUMBER solution.

The simplest approach would be to use a UNIONclause

select Reg_No, Student_Name, Subject1, Total from YourTable union all
select Reg_No, Student_Name, Subject2, Total from YourTable union all
select Reg_No, Student_Name, Subject3, Total from YourTable union all
select Reg_No, Student_Name, Subject3, Total from YourTable

UNION

Combines the results of two or more queries into a single result set that includes all the rows that belong to all queries in the union. The UNION operation is different from using joins that combine columns from two tables.

The following are basic rules for combining the result sets of two queries by using UNION:

•The number and the order of the columns must be the same in all queries.

•The data types must be compatible.

Check this Fiddle

;WITH MyCTE AS
(
    SELECT    * 
    FROM      (
                  SELECT    Reg_No, 
                            [Subject1], 
                            [Subject2], 
                            [Subject3], 
                            [Subject4]
                  FROM      Table1
              )p
    UNPIVOT 
    ( 
        Result FOR SubjectName  in ([Subject1], [Subject2], [Subject3], [Subject4])
    )unpvt
)

SELECT    T.Reg_No,
          T.Student_Name,
          M.SubjectName,
          M.Result,
          T.Total
FROM      Table1 T
          JOIN MyCTE M
              ON T.Reg_No = M.Reg_No

If you do want NULL values in the rest, you may try the following:

This is the new Fiddle

And here is the code:

;WITH MyCTE AS
(
    SELECT    * 
    FROM      (
                  SELECT    Reg_No, 
                            [Subject1], 
                            [Subject2], 
                            [Subject3], 
                            [Subject4]
                  FROM      Table1
              )p
    UNPIVOT 
    ( 
        Result FOR SubjectName  in ([Subject1], [Subject2], [Subject3], [Subject4])
    )unpvt
),
MyNumberedCTE AS
(
    SELECT    *,
              ROW_NUMBER() OVER(PARTITION BY Reg_No ORDER BY Reg_No,SubjectName) AS RowNum
    FROM      MyCTE
)
SELECT    T.Reg_No,
          T.Student_Name,
          M.SubjectName,
          M.Result,
          T.Total
FROM      MyCTE M
          LEFT JOIN MyNumberedCTE N
              ON N.Reg_No = M.Reg_No
              AND N.SubjectName = M.SubjectName
              AND N.RowNum=1
          LEFT JOIN Table1 T
              ON T.Reg_No = N.Reg_No